Photodetection of non-opaque objects transported along a conveyor by use of a light blocking opaque flap

ABSTRACT

Photodetection of the passage of transparent or translucent sheets along a conveyor is effected by placing an opaque flexible flap in the path of movement of the sheets on the conveyor. The flap is engaged and moved forward by the sheets a short distance along the conveyor, into the photodetector light path.

United States Patent [1 1 Laskowski PHOTODETECTION OF NON-OPAQUE OBJECTS TRANSPORTED ALONG A CONVEYOR BY USE OF A LIGHT BLOCKING OPAQUE FLAP Inventor: Kenneth W. Laskowski, Fairport,

Assignee: Xerox Corporation, Stamford,

Conn.

Filed: May 8, 1972 Appl. No.: 251,493

US. Cl 250/223, 250/231, 250/237 Int. Cl. H01j 3/14 Field of Search 250/223, 222, 229,

250/231, 219 D, 219 LG, 219 DO, 221, 237; 350/209; 356/71 Dec. 11, 1973 Primary Examiner-1-1arold A. Dixon Attorney-James J. Ralabate et a1.

[57] ABSTRACT Photodetection of the passage of transparent or translucent sheets along a conveyor is effected by placing an opaque flexible flap in the path of movement of the sheets on the conveyor, The flap is engaged and moved forward by the sheets a short distance along the conveyor, into the photodetector light path.

3 Claims, 6 Drawing Figures PHOTODETECTION OF NON-OPAQUE OBJECTS TRANSPORTED ALONG A CONVEYOR BY USE OF A LIGHT BLOCKING OPAQUE FLAP INTRODUCTION AND SUMMARY OF INVENTION The present invention relates to the photoelectric detection of articles, and more particularly to the photoelectric detection of the movement of a transparent or translucent article passed a detection point.

It is quite common, for example in the sheet feeding art, to transport single sheets along a conveyor, and to detect photoelectrically the arrival of the leading edge of each sheet at a reference point, and the passage of the trailing edge thereof. This is normally accomplished by placing a photosensor above or below the conveyor, and a light source opposite thereto and in position to illuminate the photosensor. When a sheet, such as paper, is carried by the conveyor passed this photodetector, it interrupts the light path from the light source to the photosensor, thereby effecting detection of the ar rival of its leading edge and the passing of its trailing edge. This action is dependent upon the sheet being relatively opaque to the passage of light, and adequate or reliable results will not be obtained if the sheet is transparent or translucent. Dependency upon the sheet alone may also create problems if the sheet is perforated.

In accordance with the present invention, an opaque light interrupter is positioned in the path of the conveyor and is adapted to be moved into the photodetector light path by the article to be detected, to cut off the illumination of the photosensor regardless of the light transmission characteristics of the article. Accordingly, transparent or translucent articles will be detected, and any perforations or light windows in the article will not affect the photodetection process.

It is therefore one object of the present invention to provide for the photoelectric detection of the movement of articles past a detection point.

Another object of the present invention is to provide for such detection regardless of the opacity or transparency of the article.

Other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of one illustrative and exemplary embodiment of the invention, had in conjunction with the accompanying drawings, in which like reference characters refer to like or corresponding parts, and wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view of a'conveyor and photodetector arrangement embodying the principles of the present invention;

FIG. 2 is a top plan view of the system shown in FIG. 1; and

FIGS. 3A-D illustrate the step by step effect of the traverse of a sheet along the conveyor and past the photodetector of FIG. 1.

, DETAILED DESCRIPTION In the drawings, an endless belt conveyor'lo is shown, having a pair of end drums 11 and 12, about which run the transversely spaced endless belts 13. Also shown are a pair of feed rolls 14 for delivering sheets 15 to one end of the conveyor 10, and a pair of between the light source 21 and photosensor 22, illumination of the photosensor is interrupted, and the presence of the object is thus detected. However, if sheets 15 are transparent or translucent, operation of the photodetector 20 is ineffective or unreliable. Pursuant to the present invention a piece of flexible opaque material 23, which may for example be a fabric or plastic sheet, is suspended from a support bar 24, and depends therefrom pastthe level of the upper flight of the conveyor 10, into the path of any oncoming objects on the conveyor. The arrival of an object pushes this flap 23 into the light path from the light source 21 to the photosensor 22, thereby detecting the arrival of the object. Referring to the sequence of occurrences shown in FIGS. 3A-D, it will be observed in FIG. 3A that as the leading edge of a sheet 15 approaches the photodetector 20, the flap 23 hangs down from bar 24 below and between the upper flight of belts 13 of conveyor 10, leaving the light path unobstructed from light source 21 to photosensor 22. As this sheet 15 continues to advance, its leading edge engages the flap 23 and carries the depending portion of the flap along with it into the position shown in FIG. 38, where the opaque flap 23 interrupts the light path from source 21 to photosensor 22. This condition prevails as the sheet 15 continues past this detection station, as shown in FIG. 3C. When the trailing edge of sheet 15 has passed the detection point, as shown in FIG. 3D, the sheet no longer supports the flap 23, and it falls free between the belts 13 of conveyor 10, thus removing any obstruction to the light path from light source 21 to photosensor 22.

The foregoing system is intended to function for the detection, particularly, of transparent sheets of thin those skilled in the art, and such modifications as are film material, or translucent paper, or perforated paper. However, it will be apparent that the concept of the invention may be used for other types of articles to be detected along conveyor 10. It will therefore be appreciated that various modifications of the described embodiment of the invention will become apparent to embraced by the spirit and scope of the appended the present invention.

What is claimed is:

1. In combination, a conveyor and a photodetector for detecting the passage of spaced articles along said conveyor, said photodetector comprising a photosensor on one side of said conveyor, a light source on the other side of said conveyor positioned to illuminate said photosensor, and a movable opaque element mounted above said conveyor and adjacent said photosensor and light source on the upstream side thereof in the path of articles on said conveyor, said opaque element normally lying outside the light path from said light source to said photosensor, whereby said element is moved between said light source and photosensor by the passage of each article along said conveyor past said photodetector.

2. In the combination set forth in claim 1, said opaque element being a flexible flap depending from a support above said conveyor.

3. In the combination set forth in claim 2, said flap depending through said conveyor and below it by an light path.

a: :u a: i: 

1. In combination, a conveyor and a photodetector for detecting the passage of spaced articles along said conveyor, said photodetector comprising a photosensor on one side of said conveyor, a light source on the other side of said conveyor positioned to illuminate said photosensor, and a movable opaque element mounted above said conveyor and adjacent said photosensor and light source on the upstream side thereof in the path of articles on said conveyor, said opaque element normally lying outside the light path from said light source to said photosensor, whereby said element is moved between said light source and photosensor by the passage of each article along said conveyor past said photodetector.
 2. In the combination set forth in claim 1, said opaque element being a flexible flap depending from a support above said conveyor.
 3. In the combination set forth in claim 2, said flap depending through said conveyor and below it by an amount greater than the distance along said conveyor between said flap and the light path from said light source to said photosensor, whereby the passage of a thin sheet along said conveyor moves said depending flap along the path of said conveyor to obstruct said light path. 